Ceres and Vesta in 2014

Posted by Richard Miles at 16:42 on 2014 Jan 04

Thanks for this Graham.I must mention that back in 2012 October, Jean Meeus added the following comment to an e-mail note about the opposition brightnesses of Ceres and Vesta:"There is something else that is interesting about Ceres and Vesta.In April 2014, these two asteroids will reach opposition with theSun at a time inteval of less than 48 hours. During almost eightmonths they will stay less than 5 degrees from each other in thesky, and during almost two months at less than 2 degrees.On 2014 July 5 their angular separation will be only 10 arcminutes,their least angular distance since at least the year 1800."Jean MeeusSince we know that Vesta changes colour slightly as it rotates, whereas Ceres does not, it would be useful to verify whether these changes can be detected photometrically. Maybe the easiest way of doing this is to do a time-series of images using a DSLR camera with enough FOV that both objects are on the same frame and then to extract the Red, Green and Blue FITS files and measure the relative B-V, V-R and B-R magnitude of Vesta relative to Ceres vs. time. Vesta rotates in just 5.34 hours so a 6-hr run should follow more than an entire rotation.

Posted by Richard Miles at 17:47 on 2014 Jan 05

Alex – The lightcurve amplitude of Vesta is small, like you say, at between 0.08-0.19 mag depending on its heliocentric longitude for the present apparition. That of Ceres ranges from 0.02-0.06 mag.By doing colour difference magnitudes, such as (B-R) for Vesta MINUS (B-R) for Ceres, any variation in general brightness of the two objects cancels out and we are left with colour changes only. Since DSLRs do 3 colours at a time, and these asteroids are both brighter than magnitude 8.5 (Vesta reaches mag 5.7 in April), these cameras are pretty ideal tools for the job. The only thing to watch will be to use a short enough exposure time to avoid saturating pixels in the image of Vesta.I’ll look to write a short ‘How To’ crib sheet for folk planning on having a go. If several people tried it then the combination of all would be better than an effort by one person only.There might be a spin-off too in that it could kick start more use of DSLRs for variable star observations as well as those of asteroids!

Posted by Steve Holmes2 at 17:19 on 2014 Jan 06

Further to Jean Meeus’ comment, I make it that their closest encounter will in fact be on 7th July – just 6arc-minutes! Not all that high in the sky and with a waxing Moon around, but an historic encounter nonetheless.

Posted by Steve Holmes2 at 00:23 on 2014 Jan 08

Thanks Richard – a timely (and indeed salutary!) reminder that if one is going to look for close approaches of minor bodies it might be a good idea to make sure your ephemerides are up to date! On investigation, mine were not. Having updated them from the MPC data (and checked them using Solex 11), I find the same result as given in your post.So, as that well-loved radio programme used to say: "I’m sorry, I’ll read that again – I make the closest approach 10arc-sec on 5th July"!!